D-Link DIR-615 Wont Connect

Hi,

I have a D-Link DIR-615 router and have set it up and managed to connect wirelessly through my laptop and phone and one of my housemates laptops, however I am unable to connect through two of my other housemates laptops. Both have previously been able to connect to the router, but I had to restore it to factory settings this afternoon, and now neither are able to.

Does anyybody have any idea why this might be?

Thanks.

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